DISSERTATION RESEARCH:Sea level rise and vegetation regime shifts: implications for soil carbon storage and vulnerability in coastal wetlands

沿海湿地过滤水，缓冲海岸线免受风暴的影响，提供重要的栖息地，并且对于全球碳储存具有重要意义。湿地土壤中的碳储存可以是长期的，并通过增加沉积物海拔的变化来影响湿地在海平面上升期间是否持续存在。气候变化和当地淡水管理正在增加咸水向沿海淡水湿地的流动，改变湿地的条件并导致那里生长的植被类型发生变化。在许多热带和亚热带沿海湿地，红树林正在取代以草为主的沼泽，这对土壤储存碳的能力产生了不确定的影响。沿海湿地尤其如此，因为它们对海平面上升很敏感。本研究的目的是确定湿地土壤碳储存的变化以及沿海湿地从以草为主的沼泽转变为红树林时向大气中释放的二氧化碳和甲烷气体的变化。研究结果将为当地佛罗里达大沼泽地以及世界各地沿海湿地的保护和恢复提供有价值的信息。此外，这些发现将使人们对不断变化的世界中植物和土壤的相互作用以及生态系统功能有更广泛的了解。该项目将在佛罗里达国际大学的一项外展活动“Marsh Mangress”期间，为当地高中生提供识别和种植湿地植物以及恢复城市沿海湿地的科学经验。这项活动还将为本科生提供在少数族裔占多数的机构的实验室和现场经验。 这项研究将利用佛罗里达州那不勒斯 10,000 个岛屿国家野生动物保护区的植被梯度，其中海平面上升和淡水操纵导致植被变化和红树林侵蚀，以了解非生物条件的变化和植被状态的变化如何随时间改变碳储存。变化的碳储量将通过当前有机碳储量（地上和地下生物量、土壤碳含量）、投入（根系生产力、沉积物表面增生）和碳损失（有机碳分解率、气体通量测量）、过去碳封存率（放射性土壤测年）和未来潜在碳损失率（代表淡水恢复或持续咸水入侵的有机物相互移植）来衡量。具体来说，该项目的目标是： 1）确定以咸水沼泽、咸水沼泽和红树林为主的植被群落为主的湿地之间碳储存、吸积和气体通量的差异。 2) 确定哪些非生物和生物机制导致湿地类型之间土壤碳动态的差异。 3) 根据土壤测年和历史航空摄影建立红树林侵蚀的时间序列，量化红树林建立以来的时间对土壤碳储存、增生和气体通量的影响。

Coastal wetlands filter water, buffer the coastline from storms, provide important habitat and are globally important for the storage of carbon. Carbon storage in wetland soils can be for the long-term and influences whether wetlands will persist during sea level rise by increasing a change in sediment elevation. Climate change and local freshwater management are increasing the movement of saltwater into coastal freshwater wetlands, altering the conditions of the wetlands and causing shifts in the types of vegetation growing there. In many tropical and subtropical coastal wetlands, mangroves are replacing grass-dominated marshes, with uncertain effects on the capability of soils to store carbon. This is especially true of coastal wetlands, because of their sensitivity to sea level rise. The goals of this study are to identify changes in the storage of carbon in wetland soils and releases to the atmosphere of the gases carbon dioxide and methane that occur as coastal wetland change from marshes dominated by grasses to mangrove forests. The research findings will provide valuable information for the conservation and restoration of the Florida Everglades locally as well as coastal wetlands throughout the world. Furthermore, the findings will provide a broader understanding of plant and soil interactions and ecosystem function in a changing world. The project will provide hands on scientific experience identifying and growing wetland plants and restoring urban coastal wetlands for local high school students during "Marsh Mangress", an outreach activity at Florida International University. This activity will also provide undergraduate students with laboratory and field experience at a majority minority institution. This research will utilize a vegetation gradient in 10,000 Islands National Wildlife Refuge in Naples, FL in which sea level rise and freshwater manipulation have driven vegetation change and mangrove encroachment, in order to understand how changing abiotic conditions and vegetation state change alter carbon storage through time. Changing carbon storage will be measured as current organic carbon stocks (above and belowground biomass, soil carbon content), inputs (root productivity, sediment surface accretion) and carbon losses (breakdown rates of organic carbon, gas flux measurements), past carbon sequestration rate (radiometric soil dating), and potential future rates of carbon loss (reciprocal transplant of organic matter to represent freshwater restoration or continuing saltwater intrusion). Specifically, the goals of this project are to: 1) Identify differences in carbon storage, accretion, and gas flux among wetlands dominated by brackish marsh, saltwater marsh, and mangrove-dominated vegetation communities. 2) Determine which abiotic and biotic mechanisms drive differences in soil carbon dynamics among wetland types. 3) Quantify the effect of time since mangrove establishment on soil carbon storage, accretion and gas flux by establishing a chronosequence of mangrove encroachment based on soil dating and historic aerial photography.